This present invention relates to a circuit configuration for monitoring the final control circuitry stages of a plurality of electrically or electromagnetically operable valves such as the braking pressure control valves of an anti-lock control system and/or of a traction slip control system, wherein the final stages are fed with short test pulses in accordance with a predetermined pattern.
Monitoring individual components and circuits for proper condition and proper operation in particular is of major importance in apparatus or systems which are critical in terms of safety such as automotive vehicle brake systems with an anti-lock control system (ABS) or a traction slip control system (ASR). An imminent failure of control, namely must be recognize and signalized in order to warn the driver and to at least ensure braking without defection control by switching off the failed control system.
A number of circuit configurations for monitoring the entire anti-lock control system and individual circuit elements or components are known. See, for example, German Patent Specification (DE-PS) No. 26 12 356, German Published Patent Application (DE-OS) No. 32 34 637. Among the critical components of an anti-lock control system for safety are the braking pressure control valves by means of which the braking pressure is kept constant, reduced and reincreased in the event of control. Typically, electromagnetically operable hydraulic valves are used for this braking pressure control operation. A defect in the actuation circuit, an electrical by-path or a leakage current should to be recognized immediately since such a defect can jeopardize control or even the braking operation itself.
Since a brake system always requires a large number of such braking pressure control valves, such as six or eight wheel valves (inlet valves and outlet valves) and further valves for controlling the auxiliary pressure, there is a need for a monitoring circuit requiring only few components per valve and a small number of elements overall. It is thus an object of this invention to develop such a circuit configuration while requiring only a small number of connections and arrangements of wiring within the electronic control unit.